Watson GW-1 Windwagon

The Watson WG-1 Windwagon is a single-seat recreational ultralight designed in the United States in 1976 and marketed for homebuilding. Designer Gary Watson originally sold kits as well as plans, but later sold only plans.

Design and development
The Windwagon is a low-wing cantilever monoplane of conventional design with fixed, tricycle undercarriage, and a single-seat open cockpit. Construction is of pop-riveted metal throughout. The outer wing panels are removable to facilitate hangering and trailering.

Power is supplied by an air-cooled, tractor-mounted piston engine driving a propeller. The engine selected by Watson was an automotive Volkwagen air-cooled engine sawn in half across its crankcase to turn the flat-four engine into a flat-two  (a modification called a "half VW"). Plans for the Windwagon included instructions for modifying a Volkswagen engine this way.

By 1987, Watson had sold over 1,025 sets of plans, and over 500 Windwagons had been built around the world.

The Hummel Bird is a development of this design.